Powering a 5000 BTU Window AC Off Grid With an Inverter

[Chef Duane]

My rig did not come with an inverter so I can only run my 5000btu window mount AC unit when I am on shore power. However, I'd like to do a little off grid camping and still like to enjoy the AC. I've got a 300ah lifepo4 battery and 200w of solar up top so I am sized appropriately. The AC unit just plugs into a duplex outlet integrated into the RV wiring. Simplest way is to run cables off the battery to the inverter and then an extension cord (sized appropriately) to where the AC plugs into the duplex. That way when I'm on shore power I plug into the duplex outlet and when I'm off grid the AC gets plugged into the inverter extension. I won't have to penetrate any exterior walls or bulkheads to do this - I'll use the existing holes and then use spray foam to seal them back up again. Configuration is below. Anyone ever do this? Any suggestions or recommendations? Any input appreciated. Then I need to put together a parts and equipment buy list.

 

[John From Detroit]

Fairly common. Question do you have a built in generator (yes/NO) It affrects my answer.

Yes: then you have some kind of transfer switch, Be it an automatic transfer system or what I call a "poor man's transfer switch) (An outlet you plug the shore cord into to use the genny

If NO then you can "Lug" a porotable and use the poor man's transfer method Why do I say this

There is a red rectangle where Shore and Inverter come together in your diagram

This needs to be a switch. Three types
One: Automatic (30 amp ATS systems are out there) it really does not matter which input you make LINE and which Generator .. Usually on an ATS Generator rules (if it's on it's selected) so I'd put SHORE into that port/connections. for your install.

MANUAL (Way less expensive) 30 amp DPDT transfer switch from your local electrical supply)

Poor man's Two outlets (20 amp will work here) one hooked to the mains. one via a breaker to teh inverter, labeled, transfer the plug as needed (how I did it in fact on one of my AC's)

Home is where I park it!

 

[Gary RV_Wizard]

That extension cord serves nicely as your "poor man's transfer switch", transferring power easily and safely. Just turn the a/c off before unplug/re-plug.

Will there be a shore-power-based charger for that battery or will it be solar charged only??

 

[bigbAZ]

I did a similar thing for the microwave but I used a slightly different way to bring the power into the microwave cabinet. My inverter is very close to the battery box so the 2/0 supply conductors are only 2 feet each. This is important because if you end up with too much voltage drop on a heavy load your inverter could shut down. Plan for less than 1% VD if possible using the Blue Sea Circuit Wizard.

Next I mounted an inlet with a 6 foot cord on the side of the fridge cabinet near the inverter. The cord end comes out in the cabinet where the micro plugs in so we just switch it around like you are planning. I have a 1 foot extension cord to connect the inverter to the inlet. I did this because it is neater, I didn't want to have a cord hanging out of a hole.

Your plan should work though, just wanted to throw the idea out there. What's the current/wattage of the AC unit? Is it inverter based? I have a small portable inverter AC unit that draws 900 watts so that's 75 amps out of the battery which won't give much more run time than a few hours depending on available charge levels.

 

[bigbAZ]

OK I just noticed you provided the model # of the AC, 450 watts, not bad. It is not inverter based though so the question would be what the inrush current is when the compressor and fan both start and can the 2000 watt inverter handle that, and if can handle it on a fully charged battery what about when the battery starts to get depleted and the voltage drops? Looking on Google it says inrush on a 450 watt window unit can be up to 1350 watts so maybe yes. I would definitely test it though before installation.

 

[Primerump]

On one of my previous rv's I fitted a cargo box on the tongue and instaled the inverter in there with the battery and fuses etc.. on the side of the box i fitted a 30 amp socket. this was as Gary said, " a poor mans transfer switch". when i needed shore power i just connected the shore lead to the front box and it powered the entire rv. I did not have to cut,drill or modify the rv in any way.

 

[Chef Duane]

Fairly common. Question do you have a built in generator (yes/NO) It affrects my answer.

I do not have a built-in generator on my rig. The red box is not an actual HW item, it's just used as a placeholder on the logic chart. The AC unit has a standard 120v 3 prong plug coming out of it and if I was going to use an inverter I would just change the plug to an appropriately sized extension cord between the inverter and the AC unit.

However, I have decided to forego this and pursue a different solution. See below.

 

[Chef Duane]

That extension cord serves nicely as your "poor man's transfer switch", transferring power easily and safely. Just turn the a/c off before unplug/re-plug.

Will there be a shore-power-based charger for that battery or will it be solar charged only??

There is a charger for the battery when connected to shore power.

 

[Chef Duane]

Thanks for all the input but after running the numbers I have decided to forego the inverter option. Even when fully charged running the AC off the battery only provides about 5-6 hours of runtime, if that. My plan was to get enough power to run the AC overnight - I am in Texas and I can personally stand the heat during the day but during the overnight hours it is intolerable. I sized up the power requirements (start up ~ 12k-15kw, continuous ~ 500w) and have ordered a generator/inverter that should fit the bill just fine. 2500w startup and 1900w continuous that should run the AC unit as long as I feed the genset gas. It was more dollars over what the inverter option was but should fit the bill nicely.

Again, thanks for all the feedback.

 

[John From Detroit]

I do not have a built-in generator on my rig. The red box is not an actual HW item, it's just used as a placeholder on the logic chart. The AC unit has a standard 120v 3 prong plug coming out of it and if I was going to use an inverter I would just change the plug to an appropriately sized extension cord between the inverter and the AC unit.

However, I have decided to forego this and pursue a different solution. See below.

Ah that's what I and I've seen at least one other call a "Poor man's transfer switch"

Not only is it the lowest cost option.
IT's also the most reliable.

Good choice.

 

[Chef Duane]

Follow up; This is the generator that I went with. 2500w peak/1900 Surge. Will power the AC unit with no issues.

 

[RayIN]

Duane, have you considers 12VDC air conditioners, some are even heat pumps. This option eliminates the need for a large inverter and the accompanying conversion power loss. Converting from 12VDC to 120VAC involves the 10X rule. You need 10X the battery amps to run an AC appliance, it is not a 1-1 ratio.

https://rvproperly.com/recommendations/appliances/best-12v-rv-air-conditioners/

 

[Chef Duane]

Duane, have you considers 12VDC air conditioners, some are even heat pumps. This option eliminates the need for a large inverter and the accompanying conversion power loss. Converting from 12VDC to 120VAC involves the 10X rule. You need 10X the battery amps to run an AC appliance, it is not a 1-1 ratio.

https://rvproperly.com/recommendations/appliances/best-12v-rv-air-conditioners/

Yes I looked at that but it I already have a functioning AC unit that works fine. If it ever craps out on me I'll look at a DC unit. The generator/inverter set up is what I'm going to run for the foreseeable future. Also, the hole in the side of the rig is sized for the current AC I have and I don't necessarily want to pull it out of there unless I absolutely have to and start modding or cutting into the wall to make a new unit fit. Thanks for the feeback!

 

[Crik Walker]

I might add that, depending on your RV's converter/charger size, you might be able to recharge your battery(s) whilst running the genny. This is what I do when running my 2100W/1600W cont. generator, primarily to recharge the Battery bank but I'll switch the Absorb Fridge to AC, saves the propane a bit, I'll also charge the cordless drill or any other low wattage device.
The only issue possibly is the noise of a genset running flat out, never an issue for me as I have no niebours and ill place it 30' away.

 

[Firstime RVer]

I might add that, depending on your RV's converter/charger size, you might be able to recharge your battery(s) whilst running the genny. This is what I do when running my 2100W/1600W cont. generator, primarily to recharge the Battery bank but I'll switch the Absorb Fridge to AC, saves the propane a bit, I'll also charge the cordless drill or any other low wattage device.
The only issue possibly is the noise of a genset running flat out, never an issue for me as I have no niebours and ill place it 30' away.

Our rooftop AC quit working in july one year and we put together a 5,000 btu window unit that just dropped into our escape window. It was mid july. The little champion 2000 watt genny sitting 20 feet away just purred all night.. Kept cool and we slept well.
We got our rooftop fixed afterwards. But I swear that window unit kept us cool enough and it was half as loud as our rooftop unit, even with the genny running.
Just my $.02 FWIW

 

[Crik Walker]

Our rooftop AC quit working in july one year and we put together a 5,000 btu window unit that just dropped into our escape window. It was mid july. The little champion 2000 watt genny sitting 20 feet away just purred all night.. Kept cool and we slept well.
We got our rooftop fixed afterwards. But I swear that window unit kept us cool enough and it was half as loud as our rooftop unit, even with the genny running.
Just my $.02 FWIW

So true, my worst noise intrusion by far was in our 2011 Berkshire 390 BH. The 8500W genset in the nose was noticeable when running, being a diesel it didn't wail like a gas unit but my God the roof AC units were ridiculously loud. Conversations were strained, hearing the TV was a noticeable challenge to the point we seldom ran the front unit at all while we were home. I'd run the rear AC with an upright fan moving air forward from the rear bedroom.
I definitely wouldn't have bought this MH if I'd known.
This influenced my decisions going forward of course, our next MH, a Winnebago 30'r, placed the AC unit in the rear passenger side compartment next to the diesel engine. Best AC I ever had, whisper quiet and a powerful unit.
My little 2100W genny at full revs/30+ ft away, is affectively unnoticeable by having the radio on. That I can live with but I would never do this in a Campground setting, even if it was allowed. Just not cool.